The static Reflect.preventExtensions() method prevents new properties from ever being added to an object (i.e. prevents future extensions to the object). It is similar to Object.preventExtensions(), but with some differences.




The target object on which to prevent extensions.

Return value

A Boolean indicating whether or not the target was successfully set to prevent extensions.


A TypeError, if target is not an Object.


The Reflect.preventExtensions method allows you to prevent new properties from ever being added to an object (i.e. prevents future extensions to the object). It is the same method as Object.preventExtensions().


Using Reflect.preventExtensions()

See also Object.preventExtensions().

// Objects are extensible by default.
var empty = {};
Reflect.isExtensible(empty); // === true

// ...but that can be changed.
Reflect.isExtensible(empty); // === false

Difference to Object.preventExtensions()

If the first argument to this method is not an object (a primitive), then it will cause a TypeError. With Object.preventExtensions(), a non-object first argument will be coerced to an object at first.

// TypeError: 1 is not an object

// 1


Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'Reflect.preventExtensions' in that specification.
Standard Initial definition.
ECMAScript Latest Draft (ECMA-262)
The definition of 'Reflect.preventExtensions' in that specification.

Browser compatibility

Update compatibility data on GitHub
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
Basic supportChrome Full support 49Edge Full support 12Firefox Full support 42IE No support NoOpera Full support 36Safari Full support 10WebView Android Full support 49Chrome Android Full support 49Edge Mobile Full support YesFirefox Android Full support 42Opera Android Full support 36Safari iOS Full support 10Samsung Internet Android Full support 5.0nodejs Full support 6.0.0


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See also

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Last updated by: wbamberg,